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VB.NET IComparable ExampleImplement the IComparable generic interface. Use the List Sort subroutine.
IComparable. How can we compare 2 objects? With the IComparable interface, we implement CompareTo and return an Integer. This indicates which object comes before the other.
Integer
Implements keyword. In VB.NET, we must use the implements keyword to specify that we want to use this interface. Then we must add a CompareTo function.
Function
Interface
Example. We introduce a class called Box. We specify that this class Implements IComparable and we specify Box as the generic type parameter.
Size The Size property is also shown. It has public Get and Set parts. We use Size to sort the Box objects.
Property
CompareTo Next we implement CompareTo. Please notice its syntax. I added an underscore to break the lines.
And In CompareTo, we simply use the Size property of the Box object to return an Integer value.
Result The value one means more than (after). The number zero means equal. And minus one means less than (before).
Class Box Implements IComparable(Of Box) Public Sub New(ByVal size As Integer) sizeValue = size End Sub Private sizeValue As Integer Public Property Size() As Integer Get Return sizeValue End Get Set(ByVal value As Integer) sizeValue = value End Set End Property Public Function CompareTo(other As Box) As Integer _ Implements IComparable(Of Box).CompareTo ' Compare sizes. Return Me.Size().CompareTo(other.Size()) End Function End Class Module Module1 Sub Main() ' Create list of Box objects. Dim boxes As List(Of Box) = New List(Of Box) boxes.Add(New Box(100)) boxes.Add(New Box(90)) boxes.Add(New Box(110)) boxes.Add(New Box(80)) ' Sort with IComparable implementation. boxes.Sort() For Each element As Box In boxes Console.WriteLine(element.Size()) Next End Sub End Module
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Code info. In Main, we create a List with 4 Box objects in it. We use New to specify the sizes of the boxes in the creation expression. We then invoke the Sort Sub.
List
Sub
And Sort internally calls the CompareTo method we implemented. It operates upon the IComparable interface.
Thus The Box class can be sorted through its IComparable interface. The Sort method itself has no special knowledge of the Box.
Result In the results, our Box objects are sorted by size, from lowest to highest. This is called an ascending sort.
Tip For a descending sort, try reversing the order you compare variables in the CompareTo function.
Summary. Some classes are rarely sorted. But for classes that are stored in groups (like in Lists), consider adding the IComparable interface.
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